Collisional broadening compensation using real or near-real time validation in spectroscopic analyzers

ABSTRACT

Validation verification data quantifying an intensity of light reaching a detector of a spectrometer from a light source of the spectrometer after the light passes through a validation gas across a known path length can be collected or received. The validation gas can include an amount of an analyte compound and an undisturbed background composition that is representative of a sample gas background composition of a sample gas to be analyzed using a spectrometer. The sample gas background composition can include one or more background components. The validation verification data can be compared with stored calibration data for the spectrometer to calculate a concentration adjustment factor, and sample measurement data collected with the spectrometer can be modified using this adjustment factor to compensate for collisional broadening of a spectral peak of the analyte compound by the background components. Related methods, articles of manufacture, systems, and the like are described.

CROSS-REFERENCE TO RELATED APPLICATIONS

The current application is related to co-pending and co-owned U.S.patent application Ser. No. 13/026,921 and co-owned U.S. patentapplication Ser. No. 13/027,000 and to co-owned U.S. Pat. No. 7,508,521,co-owned U.S. Pat. No. 7,704,301, and co-owned U.S. Pat. No. 7,819,946.The disclosure of each of the related applications and patents isincorporated herein by reference in its entirety.

TECHNICAL FIELD

The subject matter described herein relates to compensation for theeffects of collisional broadening on measurements, for example fordetection and/or quantification of trace gases, made by spectroscopicanalyzers.

BACKGROUND

Spectroscopic analysis generally relies on detection and quantificationof emission or absorption of radiation by matter (e.g. individualmolecules in analysis of gas phase compounds). The radiation is absorbedor emitted with a particular energy determined by transitions occurringto the molecules of an analyte. For example, in infrared spectroscopy,discrete energy quanta are absorbed by molecules due to excitation ofvibrational or rotational transitions of the intra-molecular bonds. Thecollision of other molecules in a gas mixture with the emitting orabsorbing molecules and the collision between the emitting or absorbingmolecules themselves can perturb the energy levels of the emitting orabsorbing molecules and therefore cause broadening of the emission orabsorption line shape. Broadening of spectral line shapes can depend onany or all of the pressure, the temperature, and composition of the gasmixture in addition to the spectral transition and concentration of aparticular target analyte. Quantitative measurement errors can occur ifthe spectroscopic analyzer is used to measure a target analyte in asample gas with combination of pressure, temperature and composition ofbackground gas that differs from the gas mixture used to calibrate theanalyzer. These errors have been found to be a substantial challenge foroptical measurement of important trace level impurities (e.g. less thanapproximately 10,000 ppm) in natural gas quality control, petrochemicalproduction, quality control and environmental emissions control, and thelike, but are not limited to those applications. The importantimpurities can include but are not limited to water (H₂O), hydrogensulfide (H₂S), other sulfur compounds, other acids, carbon dioxide(CO₂), carbon monoxide (CO), ammonia (NH₃), acetylene (C₂H₂), otherhydrocarbons, other hydro-fluoro-chloro-carbons, and combinationsthereof.

One or more approaches can be applied to compensate for broadeningcaused by differences in pressure and temperature during quantitativetarget analyte analysis. For example, the pressure and/or temperature ofthe sample gas can be maintained sufficiently close to the calibrationgas pressure and/or temperature by proper sample conditioning, includingpressure regulation and temperature stabilization of the sample gas. Inanother example, real time measurement of pressure and temperature canbe used to compensate for the collisional broadening change by applyingtheoretical models, including but not limited to polynomial corrections,pressure temperature matrixes, chemometrics, experimental calibrations,and the like. In another example parameters of the spectroscopicmeasurement (e.g. the harmonic modulation parameters) can also beadjusted in real time to compensate for line shape broadening due tochanges in sample gas pressure. An example of such an approach isdescribed in co-owned U.S. Pat. No. 7,508,521, the disclosure of whichis incorporated herein by reference.

Direct absorption spectroscopy approaches can be used for measurement oftarget analyte concentrations exceeding approximately 10,000 ppm andbackground gas mixes which offer little or substantially no interferingabsorption at the wavelength of the target analyte spectral line.Integration over the some or all of the line shape of the target analytespectrum can provide a quantitative target analyte concentration, whichis proportional to the area of the spectral line shape but does notdepend upon the line shape itself.

However, there are currently no available approaches that provideexperimental or theoretical compensation of spectral line shape changescaused by collision of the target analyte with molecules in a gas samplehaving different mass and structure and as a result of changingcomposition of the gas sample. Compensating for spectral line shapechanges caused by changing background sample gas composition iscritically important, especially for all harmonic spectroscopyapproaches, which typically have to be used to measure target analyteconcentrations below approximately 10,000 ppm and from ppb levels (e.g.approximately 1 to 5 ppb) to parts per hundred (e.g. approximately 1% to10% or even to 75% or higher) in sample gases which include absorptionby one or more compounds present at non-negligible concentrations in thebackground and in applications in which spectrally broadly absorbinggases are present or in which accumulation of condensates on opticalsurface sin the absorbing beam path is expected to occur. As an example,pipeline corrosion protection and natural gas tariff control in theUnited States typically require measurement of water vapor (H₂O) innatural gas streams within an uncertainty limit of ±4 ppm, over a rangeof approximately 0 ppm to 400 ppm or higher. The composition of atypical natural gas stream can change over a very wide range, withmethane (CH₄) tending to vary within a mole fraction range ofapproximately 50% to 100%; carbon dioxide (CO₂) tending to vary within amole fraction range of approximately 0% to 15%; and ethane (C₂H₆),propane (C₃H₈), and butane (C₄H₁₀) combined tending to vary inaccordance with actual methane and carbon dioxide concentrations to makeup 100% of the natural gas stream.

Typical industry standard moisture analyzers based on tunable diodelaser spectrometers, for example a SpectraSensors model SS2000(available from SpectraSensors, Inc. of Houston, Tex.) or a GeneralElectric Aurora (available from GE Measurement & Control Solutions ofBillerica, Mass.) may not be capable of providing necessary measurementaccuracy over such a wide range of stream component variation due to thespectral line shape broadening caused by unknown gas sample composition.In another example, the U.S. Department of Energy (DOE) sponsored anevaluation project entitled “Development of In Situ Analysis for theChemical Industry” that was conducted by the DOW Chemical Company andthat concluded that harmonic spectroscopy tunable diode lasers are notwell suited for gas analysis applications in the chemical industry dueto their measurement sensitivity to gas composition changes. The reportdetailing the results of this study: “In-Situ Sensors for the ChemicalIndustry—Final Report,” the Dow Chemical Company, Principleinvestigator: Dr. J. D. Tate, project No. DE-FC36-o21D14428, pp. 1-37,Jun. 30, 2006, is incorporated herein by reference.

SUMMARY

In one aspect of the currently disclosed subject matter, a methodincludes receiving or collecting validation verification dataquantifying an intensity of light reaching a detector of a spectrometerfrom a light source of the spectrometer after the light passes through avalidation gas across a known path length. The validation gas includes aknown amount of an analyte compound and an undisturbed backgroundcomposition that is representative of a sample gas backgroundcomposition of a sample gas to be analyzed using a spectrometer. Thesample gas background composition includes one or more backgroundcomponents other than the analyte compound. The validation verificationdata are compared with stored calibration data for the spectrometer tocalculate a concentration adjustment factor, and the concentrationadjustment factor is used to modify sample measurement data collectedwith the spectrometer to compensate for collisional broadening of aspectral peak of the analyte compound by the background components inthe sample gas.

In interrelated aspects of the current subject matter, an apparatus caninclude a tangibly embodied machine-readable medium operable to orotherwise storing instructions that cause one or more machines (e.g.,computers, programmable processors, etc.) to perform operations asdescribed herein. Similarly, computer systems are also described thatmay include at least one processor and a memory coupled to the at leastone processor. The memory may include one or more programs that causethe at least one processor to perform one or more of the operationsdescribed herein.

In optional variations, one or more of the following features can beincluded in a method or apparatus in any feasible combination. A methodcan optionally include generating the validation gas, and an apparatuscan include a validation gas generation system. The generating of thevalidation gas (for example by a validation gas generation system) canoptionally include treating a volume of the sample gas to remove orotherwise substantially reduce a concentration of the analyte compound,and adding a known mass of the analyte compound to the treated samplegas volume. The treating of the volume of the sample gas can optionallyinclude directing the volume of the sample gas through a gas processor,which can optionally include at least one of a scrubber, a purifier, achemical converter, a chemical separator, a distillation column, aseparation column, a dryer, and the like. The known mass of the analytecompound can optionally be added (for example by a validation gasgeneration system) by a process comprising one or more of adding ameasured volume of the analyte compound as a gas, liquid, or solid tothe volume of the treated sample gas; flowing the volume of the treatedsample gas as a treated sample gas stream past an analyte compoundsource that emits the analyte compound into the treated sample gasstream at a known and controlled mass and/or volume flow rate; andadding, at a known flow rate, a gas mixture containing the analytecompound at a known concentration to the treated sample gas stream.

The calculation of the concentration adjustment factor can optionallyinclude determining one or more of a difference, a ratio, a mean squareerror (mse), a coefficient of determination (R²), a cross correlationfunction, a cross correlation integral, and a regression coefficient inone or more of a light intensity domain and a wavelength domain for oneor more parts or an entirety of the validation verification data and thecalibration data. The determining can optionally include using one ormore mathematical methods of subtracting, dividing, cross correlation,convolution, curve fitting, regression, and optimization. Thecalculation of the concentration adjustment factor can optionallyinclude application of a chemometrics-based method.

In further optional variations, an apparatus can optionally include alight source, which can include, but is not limited to one or more of atunable diode laser, a tunable semiconductor laser, a quantum cascadelaser, a vertical cavity surface emitting laser (VCSEL), a horizontalcavity surface emitting laser (HCSEL), a distributed feedback laser, alight emitting diode (LED), a super-luminescent diode, an amplifiedspontaneous emission (ASE) source, a gas discharge laser, a liquidlaser, a solid state laser, a fiber laser, a color center laser, anincandescent lamp, a discharge lamp, and a thermal emitter. An apparatuscan also optionally include a detector, which can include, but is notlimited to one or more of an indium gallium arsenide (InGaAs) detector,an indium arsenide (InAs) detector, an indium phosphide (InP) detector,a silicon (Si) detector, a silicon germanium (SiGe) detector, agermanium (Ge) detector, a mercury cadmium telluride detector (HgCdTe orMCT), a lead sulfide (PbS) detector, a lead selenide (PbSe) detector, athermopile detector, a multi-element array detector, a single elementdetector, and a photo-multiplier.

Implementations of the current subject matter can provide one or moreadvantages. For example, the flow configuration used in validating aspectroscopic measurement can impact the accuracy and repeatability ofthe validation and thus its applicability to collisional broadeningcompensation. Approaches consistent with the current subject matterenable the use of a validation stream whose composition, with theexception of the concentration of the one or more analyte compounds,closely mimics that of the sample gas in which the one or more analytecompounds are detected and/or quantified. Application of a concentrationadjustment factor as described herein can establish calibration fidelityof a spectroscopic analyzer, even with a changing background compositionof the gas being sampled. This capability can constitute a significantadvance, for example with harmonic spectroscopy, which suffers fromcollisional broadening causing reading offsets that are generallydifficult or even impossible to accurately model.

The details of one or more variations of the subject matter describedherein are set forth in the accompanying drawings and the descriptionbelow. Other features and advantages of the subject matter describedherein will be apparent from the description and drawings, and from theclaims. It should be noted that the current subject matter contemplatesboth a flowing sample gas stream and a static sample gas from which asample gas volume can be withdrawn. The term “sample gas volume” or “gasvolume” as used herein therefore refers to either a flowing volume or astatic, batch volume of gas.

DESCRIPTION OF DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of this specification, show certain aspects of the subject matterdisclosed herein and, together with the description, help explain someof the principles associated with the disclosed implementations. In thedrawings,

FIG. 1 is a process flow diagram illustrating aspects of a method havingone or more features consistent with implementations of the currentsubject matter;

FIG. 2 is a diagram illustrating aspects of a system showing featuresconsistent with implementations of the current subject matter;

FIG. 3 is a diagram illustrating aspects of another system showingfeatures consistent with implementations of the current subject matter;and

FIG. 4 is a diagram illustrating aspects of yet another system showingfeatures consistent with implementations of the current subject matter.

When practical, similar reference numbers denote similar structures,features, or elements.

DETAILED DESCRIPTION

To address the aforementioned and other potential issues with analyticalvalidation of spectroscopic measurements, implementations of the currentsubject matter can provide a trace gas generator that adds a known andtemporally consistent and stable amount of a trace analyte to a gasstream to facilitate the use of that gas stream as a validation streamfor use in validation of a spectrometer and compensation for collisionalbroadening effects that can impact the analysis. Approaches consistentwith implementations of the current subject matter can be advantageousfor in-the-field preparation of a standard validation gas for use inconjunction with systems that detect and/or quantify a concentration ofone or more trace analytes in a gas mixture that includes a complexand/or varying background of other compounds whose spectral absorbancecharacteristics may or may not overlap with those of the traceanalyte(s). Such approaches can also be advantageous for measurement ofone or more trace analytes in a toxic, environmentally incompatible, orcorrosive background, such as for example vinyl-chloride monomers (VCM),chlorine (Cl₂), ammonia (NH₃), hydrogen chloride (HCl), hydrogenfluoride (HF), hydrogen sulfide (H₂S), hydrogen arsenide (AsH₃),hydrogen phosphide (PH₃), hydrogen cyanide (HCN), and the like, forwhich previously available approaches may have required substitution ofa non-toxic gas, such as for example nitrogen (N₂), for the calibrationof the optical trace gas analyzer. Approaches consistent withimplementations of the current subject matter can also be advantageousfor measurement of one or more trace analytes in a gas mixturecontaining toxic, environmentally incompatible, or corrosive compoundsthat have to be eliminated or substituted during the calibration.

Gas sampled from a gas source can include one or more analyte compounds.Detection and/or quantification of the concentration of such analytecompounds can be performed by spectroscopic analysis. To compensate forthe effects of collisional broadening on the results of thespectroscopic analysis, the current subject matter makes use of avalidation stream that resembles the sample gas as closely as ispossible. The validation stream can be prepared by first selectivelyremoving or at least substantially reducing the concentration of theanalyte or analytes in the sample gas from the gas source and thenadding the analyte or analytes to the neat (free of the analyte oranalytes) sample gas at a well controlled and accurately known massand/or volume (note: perm tube vs. premixed bottle) delivery rate toproduce a consistent, controlled, and well known concentration of theanalyte or analytes in the validation stream. A test spectrum collectedusing this validation stream can be compared to a previously storedreference spectrum collected using the same analytical system during acalibration process. Based on this comparison, a concentrationadjustment factor can be determined to account for differences between afirst background condition, including for example chemical composition,pressure and temperature, etc., of the validation stream and a secondbackground condition of a calibration gas used to prepare the storedreference spectrum. Alternatively, a test spectrum collected using thesample stream can be compared to the test spectrum collected using thevalidation stream instead of the previously stored reference spectrum todirectly generate a more accurate concentration reading.

Analyte compounds with which implementations of the current subjectmatter can be used include, but are not limited to, hydrogen sulfide(H₂S); hydrogen chloride (HCl); water vapor (H₂O); hydrogen fluoride(HF); hydrogen cyanide (HCN); hydrogen bromide (HBr); ammonia (NH₃);arsine (AsH₃); phosphine (PH₃); oxygen (O₂); carbon monoxide (CO);carbon dioxide (CO₂); hydrocarbons, including but not limited to methane(CH₄), ethane (C₂H₆), ethene (C₂H₄), acetylene (C₂H₂), etc.; and thelike.

The flow chart 100 of FIG. 1 illustrates features of a method consistentwith at least some implementations of the current subject matter. At102, a validation gas is generated to contain one or more analytecompounds in an amount or concentration that is known or at leastwell-characterized. As used herein, the term “known” is intended torefer to a concentration, amount, or the like that is known to theextent possible in light of inherent errors in measurement of an amountor concentration of a validation gas. In some situations, it isacknowledged and one of ordinary skill in the art would readilyunderstand that it may not be feasible to “know” the amount orconcentration of the one or more analytes in a validation gas to acomplete certainty. In such cases, such an amount or concentration canin some examples be considered to be “well-characterized” if measured tothe accuracy of an available instrument or instruments or otherwiseproduced in a reasonably well-controlled and reasonably reproduciblemanner. When the term “known” is used herein in reference to aconcentration of an analyte, it should be readily understood that theforegoing explanation applies and that descriptions herein of knownconcentrations or amounts are assumed to refer to such values that areknown and/or well-characterized within a reasonable margin of error.

In an implementation, a validation gas can be generated by firsttreating a volume of a sample gas to remove or otherwise substantiallyreduce a concentration of an analyte compound in the sample gas, forexample by directing the sample gas through a gas processor, which canoptionally include but is not limited to a scrubber, a purifier, adryer, a chemical treatment or conversion process, or the like. Togenerate the known concentration of the analyte compound in the treatedsample gas volume, after treating the sample gas volume by the gasprocessor, an analyte compound can added to the treated sample gasstream at a known (or at least well-characterized) and controlled massand/or volume flow rate. A known mass of the analyte compound can beadded using one or more processes, including but not limited to adding ameasured volume of the analyte compound as a gas, liquid, or solid tothe volume of the treated sample gas; flowing the volume of the treatedsample gas as a treated sample gas stream past an analyte compoundsource that emits the analyte compound into the treated sample gasstream at a known and controlled mass and/or volume flow rate; andadding, at a known flow rate, a gas mixture containing the analytecompound at a known concentration to the treated sample gas stream.

At 104, validation verification data, for example a test spectrum, arereceived or collected for the validation gas, for example at aprogrammable processor that can be local to the spectrometer or remotelyconnected via a wired or wireless network or other communication link.The receiving of the validation verification data can occursynchronously with its generation by the spectrometer or asynchronously(e.g. with a time delay for transmission or in discrete packets ofdata). The validation verification data quantify a first intensity oflight reaching a detector from a light source after the light passesthrough the validation stream across a first known path length. Thevalidation verification data are compared at 106 with stored calibrationdata, for example a previously stored reference spectrum collected withthe same analyzer system using a reference gas of a known concentration,to calculate a concentration adjustment factor. At 110, theconcentration adjustment factor is used to modify sample measurementdata quantifying a second intensity of light reaching the detector fromthe light source after the light passes through a sample stream orvolume of sample gas across a second known path length that can includeall or part of the first known path length. The modifying of the samplemeasurement data can provide a compensation for collisional broadeningof spectral peaks of the one or more analyte compounds in the samplegas. This compensation can be used to provide a more accuratemeasurement and/or to validate a measurement of a spectral analyzerrelative to a previous calibration state.

The concentration adjustment factor can be calculated as one or more ofthe difference, the ratio, the mean square error (mse), the coefficientof determination (R²), the cross correlation function or integral, theregression coefficients in one or more of the light intensity domain andthe wavelength domain, and the like for one or more parts or theentirety of the validation verification data and the calibration datausing one or more mathematical methods of subtracting, dividing, crosscorrelation, convolution, curve fitting, regression, optimization, andthe like. The concentration adjustment factor can be used to modify thesample measurement data before or after comparing the sample measurementdata with the calibration data. The modification of the samplemeasurement data using the concentration adjustment factor can utilizeone or more mathematic methods of subtracting, dividing, crosscorrelation, convolution, curve fitting, regression and optimization.Alternatively, the sample measurement data can be compared to thevalidation verification data instead of the calibration data to directlygenerate the more accurate concentration reading. The comparison of thesample measurement data and the validation verification data can utilizeone or more mathematical methods of subtracting, dividing, crosscorrelation, convolution, curve fitting, regression, optimization, andthe like to generate the ratio between the sample measurement data andthe validation verification data.

FIG. 2 shows an example of a system 200 having features consistent withone or more implementations of the current subject matter. A lightsource 202 provides a continuous or pulsed light that is directed to adetector 204 via a path length 206. The path length 206 can traverse oneor more gas volumes. In the example system 200 shown in FIG. 2, the pathlength 206 twice traverses each of a first volume 212 and a secondvolume 214, which are contained within a single optical cell 216 thatincludes a first window or other at least partially radiationtransmissive surface 220, a second window or other radiationtransmissive surface 222, and a mirror or other at least partiallyradiation reflective surface 224 that at least partially define thefirst volume 212 and the second volume 214. Sample gas can, in someimplementations, be obtained from a gas source, which in the example ofFIG. 2 is a pipeline 226, for delivery to the first volume 212 and thesecond volume, for example via a sample extraction port or valve 230that receives the sample gas from the source and a first inlet port 232delivering gas to the first volume 212 and a second inlet port 234delivering gas to the second volume 214. Gas in the first volume 212 canexit the first volume 212 via a first outlet valve or port 236 and gasin the second volume 214 can exit the second volume 212 via a secondoutlet valve or port 240

Gas passing to the first volume 212 can be directed first through a gasprocessor 242 that removes or at least reduces a concentration of theanalyte compound in the gas flowing to the first volume 212 as a firstprocess in creating a validation stream. The gas processor 242 canadvantageously not substantially affect the concentration of at leastone background compound in the validation stream. The gas processor 242can optionally be a scrubber, a purifier, a dryer, a chemical conversionunit, or the like that reduces a concentration of the analyte compoundin the validation stream, advantageously to an at least approximatelynegligible level, for example by chemically or physically removing theanalyte compound from the gas phase to another phase (e.g. solid,adsorbed, absorbed, liquid, dissolved, etc.) or by chemically convertingthe analyte compound to another chemical species whose spectralcharacteristics differ sufficiently from those of the analyte compoundso as to not interfere with measurements at a narrow line width spectralregion focused on an absorption or emission characteristic of theanalyte compound.

The validation stream can pass from the gas processor 242 to an analytegenerator 244 that adds the analyte compound to the validation stream.In some variations, the analyte generator 244 can be one or morediffusion-type gas generators, such as for example one or more osmoticmembrane generators or permeation tubes (an illustrative example ofwhich is the G-Cal product line available from VICI Metronics ofPoulsbo, Wash.). Alternatively, the analyte generator 244 can be a mixerthat blends premixed analyte in one or more carrier gases from acompressed gas cylinder 248 with the neat sample stream flowing out ofthe gas processor 242.

The first volume 212 and the second volume 214 can in someimplementations be configured as a sample measurement cell and avalidation cell such as those illustrated and described in co-pendingand co-owned application for U.S. patent Ser. No. 13/026,921 and13/027,000, the disclosures of which are incorporated herein byreference. Other configurations are within the scope of the currentsubject matter. For example, either or both of the first volume 212 andthe second volume 214 can be free gas space, for example part or all ofthe exhaust stack of a combustion installation, chemical processingplant, etc.

As shown in FIG. 2, each of the first volume 212 and the second volume214 can be configured as separate optical cells, one for containing avolume of the validation stream, and the other for containing either anuntreated volume of the sample gas or a “zero gas” having at least oneof known and negligible first light absorbance characteristics thatoverlap second light absorbance characteristics of the analyte compoundwithin a wavelength range of the light provided by the light source 202.The zero gas can in some implementations be a gas provided from acompressed gas cylinder 246 connected to a supply line to the secondinlet port 234 via a connector port or valve 250. The zero gas canoptionally include one or more of a noble gas, nitrogen gas, oxygen gas,air, hydrogen gas, a homo-nuclear diatomic gas, at least a partialvacuum, a hydrocarbon gas, a fluoro-carbon gas, a hydro-fluoro-carbongas, a chloro-carbon gas, a chloro-fluoro-carbon gas, ahydro-chloro-carbon gas, a hydro-fluoro-chloro-carbon gas, carbonmonoxide gas, carbon dioxide gas, some other gas including knownconcentrations of one or more compounds with known, or optionally atleast well characterized, spectroscopic responses at one or morewavelengths provided by the light source 202, or the like. The zero gascan optionally be passed through a scrubber or chemical converter toremove or reduce a concentration of the trace analyte therein beforedirecting the zero gas into the path of the light.

A controller 252, which can include one or more programmable processorsor the like, can communicate with one or more of the light source 202and the detector 204 for controlling the emission of the light 206 andreceiving signals generated by the detector 204 that are representativeof the intensity of light impinging on the detector 204 as a function ofwavelength. In various implementations, the controller 252 can be asingle unit that performs both of controlling the light source 202 andreceiving signals from the detector 204, or it can be more than one unitacross which these functions are divided. Communications between thecontroller 252 or controllers and the light source 202 and detector 204can be over wired communications links, wireless communications links,or any combination thereof.

One or both of the first volume 212 and the second volume 214 can bemaintained at a stable temperature and pressure. Alternatively, one orboth of the first volume 212 and the second volume 214 can include oneor more temperature and/or pressure sensors to determine a currenttemperature and pressure within that volume for use in one or morecalculations to compensate for temperature and/or pressure changesrelative to a validation or calibration condition of the spectroscopicinstrument.

The system 200 can be operated to perform a collisional broadeningcompensation measurement as discussed above by running the validationgas through the first volume 212 and the zero gas through the secondvolume 214. To perform a measurement of the analyte concentration in thegas from the gas source, the sample gas can be directed into the secondvolume 214. During this process, the validation gas can continue to beprovided to the first volume 212. The light intensity arriving at thedetector 204 from the light source 202 after traversing the path lengthcan be corrected mathematically to account for absorption by the analytecompound present in the validation gas in the first volume 212.

In another implementation, which is illustrated in FIG. 3, a systemincludes a single volume 302 within an optical cell 216. One or moreflow switching valves or comparable devices 304 can be included on asample gas supply line from a gas source, which can be a pipeline 226 asshown in FIG. 3, some other source of sample gas, or the like. The flowswitching valves or comparable devices 304 can be switched to direct gasfrom the gas source to flow through a gas processor 242 and an analytegenerator 244 to generate a validation gas as discussed above. Thevalidation gas is delivered to the single volume 302 via the inlet portor valve 234. The system 300 can be operated to perform a collisionalbroadening compensation measurement as discussed above by running thisvalidation gas through the single volume 302. To perform a measurementof the analyte concentration in the gas from the gas source, the flowswitching valves or comparable devices 304 can be switched to direct gasto the single volume 302 via the inlet port or valve 234 without passingthrough the gas processor 242 and the analyte generator 244.

The controller 252, or alternatively one or more other processors thatare either collocated with the other components or in wireless, wired,etc. communication therewith, can perform the processing functionsdiscussed above in reference to the method illustrated in FIG. 1.

In yet another implementation, which is illustrated in FIG. 4, a system400 includes a first volume 402 and a second volume 404 included withintwo separate optical cells 406 and 410, respectively. The initial laserbeam or series of laser pulses 412 from the laser source 202 can besplit into a first split beam 414 and a second split beam 416 via a beamsplitting, demultiplexing, etc. device 420, which can include free spaceor fiber based beam splitters, gratings, fiber splitters, or otherpartial radiation transmissive and/or anti-reflective or reflectivesurfaces, which can include, but are not limited to oxides, such as forexample silicon dioxide (SiO₂), titanium dioxide (TiO₂), aluminum oxide(Al₂O₃), hafnium oxide (HfO₂), zirconium oxide (ZrO₂), scandium oxide(Sc₂O₃), niobium oxide (NbO₂), and tantalum oxide (Ta₂O₅); fluorides,such as for example magnesium fluoride (MgF₂), lanthanum fluoride(LaF₃), and aluminum fluoride (AlF₃); etc.; and/or combinations thereof;metallic materials including but not limited to gold (Au), silver (Ag),copper (Cu), steel, aluminum (Al), and the like; one or more layers oftransparent dielectric optical materials (e.g. oxides, fluorides, etc.);and/or a combination of metallic and dielectric optical materials or thelike. The first split beam 414 traverses the first volume 402 one ormore times before reaching a first detector 422. The second split beam416 transverses the second volume 404 one or more times before reachinga second detector 424.

A controller 252 controls the light source 202 and receives signals fromthe detectors 422 and 424. The system 400 can be operated to perform acollisional broadening compensation measurement as discussed above byrunning the validation gas through the first volume 402 and theuntreated sample gas through the second volume 404 at either the sametime or at different times.

In an alternative implementation of the system shown in FIG. 4, the twosplit beams 414 and 416 can be combined into a single beam, after havingexited from the first volume 402 and the second volume 404 respectively,by one or more beam multiplexing devices, which can include one or moreof gratings, fiber combiners or partial radiation transmissive and/oranti-reflective or reflective surfaces. In this implementation, themultiplexed single beam can be detected by a single detector, whichprovides signals to the controller.

Both sample measurement and the validation verification measurements asdescribed herein can optionally be used in conjunction with adifferential absorption approach, including but not limited to thosedescribed in co-owned U.S. Pat. No. 7,704,301 and co-owned U.S. Pat. No.7,819,946. When a differential absorption method is used, an analyticalsystem, for example one including one or more features shown in FIG. 2through FIG. 4 or otherwise within the scope of the current subjectmatter, can be modified to include a gas processor similar to gasprocessor 242 and one or more flow switching valves or comparabledevices similar to a device 304.

In various implementations of the current subject matter, the validationstream can be used in conjunction with a flow-through validation cellsuch as is described in co-pending and co-owned U.S. patent applicationSer. No. 13/026,921 and co-pending and co-owned U.S. patent applicationSer. No. 13/027,000. The light source 202 can include, for example, oneor more of a tunable diode laser, a tunable semiconductor laser, aquantum cascade laser, a vertical cavity surface emitting laser (VCSEL),a horizontal cavity surface emitting laser (HCSEL), a distributedfeedback laser, a light emitting diode (LED), a super-luminescent diode,an amplified spontaneous emission (ASE) source, a gas discharge laser, aliquid laser, a solid state laser, a fiber laser, a color center laser,an incandescent lamp, a discharge lamp, a thermal emitter, and the like.The detector 206 can include, for example, one or more of an indiumgallium arsenide (InGaAs) detector, an indium arsenide (InAs) detector,an indium phosphide (InP) detector, a silicon (Si) detector, a silicongermanium (SiGe) detector, a germanium (Ge) detector, a mercury cadmiumtelluride detector (HgCdTe or MCT), a lead sulfide (PbS) detector, alead selenide (PbSe) detector, a thermopile detector, a multi-elementarray detector, a single element detector, a photo-multiplier, and thelike.

Optical configurations consistent with one or more implementations ofthe current subject matter can optionally include at least one opticalfeature for transmitting and/or reflecting the beam of light 206 betweenthe light source 202 and the detector 204. Such optical components canadvantageously have a low absorbance of light at the wavelength or rangeof wavelengths at which the light source 202 emits the light. In otherwords, a reflective optical component would advantageously reflect morethan 50% of the incident light at the wavelength or in the range ofwavelengths, in a single reflection, an optical light guide wouldadvantageously transmit more than 1% of the incident light, and a windowwould advantageously be anti-reflection coated and transmit more than90% of the incident light at the wavelength or in the range ofwavelengths.

Implementations of the approach described herein can be applicable toany laser absorption spectrometer that includes a tunable laser source,including but not limited to direct absorption spectrometers, harmonicabsorption spectrometers, differential absorption spectrometers, etc.For a direct absorption spectrometer, the measurement of trace analyteconcentrations can be performed without using a harmonic conversion ordemodulation of the signal obtained from the detector. However, periodicor continuous recalibration of the laser light source, detector, etc.can be performed using a calibration circuit, etc. that makes use of aharmonic signal obtained from the detector signal.

One or more aspects or features of the subject matter described hereincan be realized in digital electronic circuitry, integrated circuitry,specially designed application specific integrated circuits (ASICs),field programmable gate arrays (FPGAs) computer hardware, firmware,software, and/or combinations thereof. These various aspects or featurescan include implementation in one or more computer programs that areexecutable and/or interpretable on a programmable system including atleast one programmable processor, which can be special or generalpurpose, coupled to receive data and instructions from, and to transmitdata and instructions to, a storage system, at least one input device,and at least one output device.

These computer programs, which can also be referred to as programs,software, software applications, applications, components, or code,include machine instructions for a programmable processor, and can beimplemented in a high-level procedural and/or object-orientedprogramming language, and/or in assembly/machine language. As usedherein, the term “machine-readable medium” refers to any computerprogram product, apparatus and/or device, such as for example magneticdiscs, optical disks, memory, and Programmable Logic Devices (PLDs),used to provide machine instructions and/or data to a programmableprocessor, including a machine-readable medium that receives machineinstructions as a machine-readable signal. The term “machine-readablesignal” refers to any signal used to provide machine instructions and/ordata to a programmable processor. The machine-readable medium can storesuch machine instructions non-transitorily, such as for example as woulda non-transient solid-state memory or a magnetic hard drive or anyequivalent storage medium. The machine-readable medium can alternativelyor additionally store such machine instructions in a transient manner,such as for example as would a processor cache or other random accessmemory associated with one or more physical processor cores.

To provide for interaction with a user, one or more aspects or featuresof the subject matter described herein can be implemented on a computerhaving a display device, such as for example a cathode ray tube (CRT) ora liquid crystal display (LCD) or a light emitting diode (LED) monitorfor displaying information to the user and a keyboard and a pointingdevice, such as for example a mouse or a trackball, by which the usermay provide input to the computer. Other kinds of devices can be used toprovide for interaction with a user as well. For example, feedbackprovided to the user can be any form of sensory feedback, such as forexample visual feedback, auditory feedback, or tactile feedback; andinput from the user may be received in any form, including, but notlimited to, acoustic, speech, or tactile input. Other possible inputdevices include, but are not limited to, touch screens or othertouch-sensitive devices such as single or multi-point resistive orcapacitive trackpads, voice recognition hardware and software, opticalscanners, optical pointers, digital image capture devices and associatedinterpretation software, and the like. A computer remote from ananalyzer can be linked to the analyzer over a wired or wireless networkto enable data exchange between the analyzer and the remote computer(e.g. receiving data at the remote computer from the analyzer andtransmitting information such as calibration data, operating parameters,software upgrades or updates, and the like) as well as remote control,diagnostics, etc. of the analyzer.

The subject matter described herein can be embodied in systems,apparatus, methods, and/or articles depending on the desiredconfiguration. The implementations set forth in the foregoingdescription do not represent all implementations consistent with thesubject matter described herein. Instead, they are merely some examplesconsistent with aspects related to the described subject matter.Although a few variations have been described in detail above, othermodifications or additions are possible. In particular, further featuresand/or variations can be provided in addition to those set forth herein.For example, the implementations described above can be directed tovarious combinations and subcombinations of the disclosed featuresand/or combinations and subcombinations of several further featuresdisclosed above. In addition, the logic flows depicted in theaccompanying figures and/or described herein do not necessarily requirethe particular order shown, or sequential order, to achieve desirableresults. Other implementations may be within the scope of the followingclaim.

What is claimed is:
 1. A method comprising: receiving validationverification data quantifying an intensity of light reaching a detectorof a spectrometer from a light source of the spectrometer after thelight passes through a validation gas across a known path length, thevalidation gas comprising a known amount of an analyte compound and anundisturbed background composition that is representative of a samplegas background composition of a sample gas to be analyzed using aspectrometer, the sample gas background composition comprisingbackground components other than the analyte compound; comparing thevalidation verification data with stored calibration data from acalibration gas for the spectrometer to calculate a concentrationadjustment factor to account for differences between a first backgroundcondition of the validation gas and a second background condition of thecalibration gas; and modifying, using the concentration adjust factor,sample measurement data collect with the spectrometer to compensate forcollisional broadening of the spectral peak of the analyte compound backthe background components in the sample gas.
 2. A method as in claim 1,wherein at least one of the receiving, the comparing, and the modifyingare performed by at least one programmable processor.
 3. A method as inclaim 1, further comprising generating the validation gas.
 4. A methodas in claim 3, wherein the generating of the validation gas comprisestreating a volume of the sample gas to remove or otherwise substantiallyreduce a concentration of the analyte compound, and adding a known massof the analyte compound to the treated sample gas volume.
 5. A method asin claim 4, wherein the treating of the volume of the sample gascomprises directing the volume of the sample gas through a gasprocessor.
 6. A method as in claim 5, wherein the gas processorcomprises at least one of a scrubber, a purifier, a chemical converter,a chemical separator, a distillation column, a separation column, and adryer.
 7. A method as in claim 4, wherein the known mass of the analytecompound is added by a process comprising one or more of adding ameasured volume of the analyte compound as a gas, liquid, or solid tothe volume of the treated sample gas; flowing the volume of the treatedsample gas as a treated sample gas stream past an analyte compoundsource that emits the analyte compound into the treated sample gasstream at a known and controlled mass and/or volume flow rate; andadding, at a known flow rate, a gas mixture containing the analytecompound at a known concentration to the treated sample gas stream.
 8. Amethod as in claim 1, wherein the calculation of the concentrationadjustment factor comprises determining one or more of a difference, aratio, a mean square error (mse), a coefficient of determination (R²), across correlation function, a cross correlation integral, and aregression coefficient in one or more of a light intensity domain and awavelength domain for one or more parts or an entirety of the validationverification data and the calibration data.
 9. A method as in claim 6,wherein the determining comprises using one or more mathematical methodsof subtracting, dividing, cross correlation, convolution, curve fitting,regression, and optimization.
 10. A method as in claim 1, wherein thecalculation of the concentration adjustment factor comprises applicationof a chemometrics-based method.
 11. A method as in claim 1, wherein thelight from the light source comprises a wavelength absorbed by theanalyte compound, and the quantified intensity of light reaching thedetector is a function of absorption of the light by the analytecompound in the validation gas across the known path length.
 12. Amethod as in claim 11 wherein the absorption of the light by the analytecompound depends on the collisional broadening effects of the backgroundcomposition of the gas sample on the spectral peak of the analytecompound.
 13. An apparatus comprising: A non-transitory machine readablemedium storing instructions that, when executed by at least oneprogrammable processor, cause the at least one programmable processor toperform operations comprising: receiving validation verification dataquantifying an intensity of light reaching a detector of a spectrometerfrom a light source of the spectrometer after the light passes through avalidation gas across a known path length, the validation gas comprisinga known amount of an analyte compound and an undisturbed backgroundcomposition that is representative of a sample gas backgroundcomposition of a sample gas to be analyzed using a spectrometer, thesample gas background composition comprising background components otherthan the analyte compound; comparing the validation verification datawith stored calibration data from a calibration gas for the spectrometerto calculate a concentration adjustment factor to account fordifferences between a first background condition of the validation gasand a second background condition of the calibration gas; and modifying,using the concentration adjust factor, sample measurement data collectwith the spectrometer to compensate for collisional broadening of thespectral peak of the analyte compound back the background components inthe sample gas.
 14. An apparatus as in claim 13, further comprising theat least one programmable processor.
 15. An apparatus as in claim 13,further comprising a validation gas generation system that generates thevalidation gas.
 16. An apparatus as in claim 15, wherein the validationgas generation system treats a volume of the sample gas to remove orotherwise substantially reduce a concentration of the analyte compound,and adds a known mass of the analyte compound to the treated sample gasvolume.
 17. An apparatus as in claim 16, wherein the validation gasgeneration system comprises a gas processor through which the volume ofthe sample gas is directed.
 18. An apparatus as in claim 17, wherein thegas processor comprises at least one of a scrubber, a purifier, achemical converter, a chemical separator, a distillation column, aseparation column, and a dryer.
 19. An apparatus as in claim 16, whereinthe validation gas generation system adds the known mass of the analytecompound by a process comprising one or more of adding a measured volumeof the analyte compound as a gas, liquid, or solid to the volume of thetreated sample gas; flowing the volume of the treated sample gas as atreated sample gas stream past an analyte compound source that emits theanalyte compound into the treated sample gas stream at a known andcontrolled mass and/or volume flow rate; and adding, at a known flowrate, a gas mixture containing the analyte compound at a knownconcentration to the treated sample gas stream.
 20. An apparatus as inclaim 13, wherein the calculation of the concentration adjustment factorcomprises determining one or more of a difference, a ratio, a meansquare error (mse), a coefficient of determination (R²), a crosscorrelation function, a cross correlation integral, and a regressioncoefficient in one or more of a light intensity domain and a wavelengthdomain for one or more parts or an entirety of the validationverification data and the calibration data.
 21. An apparatus as in claim18, wherein the determining comprises using one or more mathematicalmethods of subtracting, dividing, cross correlation, convolution, curvefitting, regression, and optimization.
 22. An apparatus as in claim 13,wherein the calculation of the concentration adjustment factor comprisesapplication of a chemometrics-based method.
 23. An apparatus as in claim13, wherein the light source comprises one or more of a tunable diodelaser, a tunable semiconductor laser, a quantum cascade laser, avertical cavity surface emitting laser (VCSEL), a horizontal cavitysurface emitting laser (HCSEL), a distributed feedback laser, a lightemitting diode (LED), a super-luminescent diode, an amplifiedspontaneous emission (ASE) source, a gas discharge laser, a liquidlaser, a solid state laser, a fiber laser, a color center laser, anincandescent lamp, a discharge lamp, and a thermal emitter.
 24. Anapparatus as in claim 13, wherein the detector comprises one or more ofan indium gallium arsenide (InGaAs) detector, an indium arsenide (InAs)detector, an indium phosphide (InP) detector, a silicon (Si) detector, asilicon germanium (SiGe) detector, a germanium (Ge) detector, a mercurycadmium telluride detector (HgCdTe or MCT), a lead sulfide (PbS)detector, a lead selenide (PbSe) detector, a thermopile detector, amulti-element array detector, a single element detector, and aphoto-multiplier.
 25. A system comprising: a light source to emit light;and a detector positioned a known path length from the light source todetect light emitted from the light source; wherein the system isconfigured to perform operations comprising: quantifying an intensity oflight reaching the detector from the light source after the light passesthrough a validation gas across the known path length, the validationgas comprising a known amount of an analyte compound and an undisturbedbackground composition that is representative of a sample gas backgroundcomposition of a sample gas to be analyzed using a spectrometer, thesample gas background composition comprising background components otherthan the analyte compound; comparing validation verification datacharacterizing the intensity of light reaching the detector with storedcalibration data from a calibration gas from the spectrometer tocalculate a concentration adjustment factor to account for differencesbetween a first background condition of the validation gas and a secondbackground condition of the calibration gas; and modifying samplemeasurement data collected with the spectrometer using the concentrationadjustment factor, to compensate for collisional broadening of thespectral peak of the analyte compound by the background components inthe sample gas.